Copper/iron/aluminium alloys

ABSTRACT

COPPER/IRON-ALUMINIUM ALLOYS OF THE BASIC COMPOSITION (WEIGHT PERCENTAGE) 35 TO 75 COPPER, 20 TO 50 IRON AND 5 TO 15 ALUMINIUM AND COMPRISING A MATRIX OF A COPPERRICH SOLID SOLUTION PHASE WHICH CONTAINS A DISPERSED IRONRICH SOLID SOLUTION PHASE, HAVE AT LEAST ONE ALLOY ELEMENT ADDITIONALLY PRESENT TO ENNOBLE THE IRON-RICH PHASE AND/OR TO PROVIDE AN ADHERENT PROTECTIVE FILM ON THE IRON-RICH PHASE. ADDITIONS SELECTED FROM THE GROUP NICKEL, CHROMIUM, TUNGSTEN, MOLYBDENUM AND COBALT, ARE MORE LIKELY TO ACT AS ENNOBLING ELEMENTS AND THOSE SELECTED FROM THE GROUP TITANIUM, NIOBIUM, TANTALUM, ZIRCONIUM AND SILICON, ARE MORE LIKELY TO BE FILM-FORMING AGENTS. PREFERABLY NOT MORE THAN ABOUT 15 PERCENT OF EACH ADDITIVE ELEMENT IS PRESENT, IN HTE CASE OF NICKEL, THE RANGE OF 3 TO 12 (WEIGHT) PERCENT IS PREFERRED AND IN HTE CASE OF CHROMIUM, 3 TO 9 (WEIGHT) PERCENT IS PREFERRED.

United States Patent Office US. Cl. 75-122 5 Claims ABSTRACT OF THEDISCLOSURE Copper/iron/aluminium alloys of the basic composition (weightpercentage) 35 to 75 copper, 20 to 50 iron and 5 to 15 aluminium andcomprising a matrix of a copperrich solid solution phase which containsa dispersed ironrich solid solution phase, have at least one alloyelement additionally present to ennoble the iron-rich phase and/ or toprovide an adherent protective film on the iron-rich phase. Additionsselected from the group nickel, chromium, tungsten, molybdenum andcobalt, are more likely to act as ennobling elements and those selectedfrom the group titanium, niobium, tantalum, zirconium and silicon, aremore likely to be film-forming agents. Preferably not more than about 15percent of each additive element is present. In the case of nickel, therange of 3 to 12 (weight) percent is preferred and in the case ofchromiurn, 3 to 9 (weight) percent is preferred.

This invention relates to alloys that are basically copper/ iron/aluminium alloys. It has been found that alloys of the composition(weight percentage) 35 to 75 copper, to 50 iron and 5 to 15 aluminiumare susceptible to hotworking to yield materials that have usefulmechanical properties. Such materials are described in British patentspecification No. 1,137,123; these materials comprise a matrix of acopper-rich aluminium-containing solid solution phase in which isdispersed an iron-rich solid solution phase also containing aluminium asdescribed in that specification. In an alloy of this kind the relativehardnesses of the two phases are such that hot-working of the alloy,possibly followed by cold-working, converts the dispersion to a fibrousform which acts as reinforcement for the matrix; the mechanicalproperties of the alloy are thereby enhanced.

It has been found that, in spite of their good mechanical properties,these alloys suffer from the point of corrosion. It is evident that itis unlikely that alloys of the basic composition will be of use, forinstance, under marine conditions and, even under ordinary atmosphericconditions, there is a tendency for loose oxide to form on the alloys.

Corrosion resistance, is, of course mainly comparative. The criterion tobe applied in assessing the value of any particular material from thepoint of corrosion resistance will vary depending largely on theenvironment in which it is intended that the material shall normally beused. The material may perform satisfactorily when subjected to thewell-known test involving immersion in a 3% saline solution and a goodrating as a result of submission to such a test may provide enoughevidence that a particular material would stand up to, say, marineconditions. However, such a test may not show that that particularmaterial may prove to be highly satisfactory from the point of beingtarnish free-that is, that it will suffer exposure and use underordinary domestic conditions without undue discolouration due to surfaceaction (this is not to say that all materials suitable for marine usewill also be tarnish free). Another material, while not being suitable3,666,448 Patented May 30, 1972 for the extremes of marine use, may behighly satisfactory for use in a corrosive atmosphere at highertemperatures than normal atmospheric temperature where perhapsresistance to scaling may be more important than resistance todiscolouration. These are all degrees of corrosion resistance and fromthe following description it will be appreciated that the object of thepresent invention is to provide alloys of the basic composition setforth above which will be more resistant to corrosion in at least one ofthese respects.

According to the invention in a copper/ iron/ aluminium alloy of thebasic composition set forth above and having a matrix of a copper-richsolid solution phase which contains a dispersed iron-rich solid solutionphase, at least one alloying element is additionally present to ennoblethe iron-rich dispersed phase and/or to provide an adherent protectivefilm on the iron-rich phase. Elements suitable as additional elementsare comprised within the groups consisting of nickel, chromium,tungsten, molybdenum and cobalt and consisting of titanium, niobium,tantalum, zirconium and silicon. The former are more likely to act asennobling elements and the latter as film forming agents though,certainly in some cases, notably in the case of chromium, the elementsmay fulfil an alternative or additional function. In the cases of nickeland chromium, for instance, it can be shown, certainly in some alloys,that chromium when added alone tends to concentrate in the iron-richphase and that nickel when added alone tends to be concentrated at aslightly higher level in the copper-rich phase. On the other hand, theaddition of both these elements in combination causes both to bepartitioned to a beneficial extent in both phases and in fact, thesolubility of both elements in the iron-rich phase is slightlyincreased. It is to be noted, however, that these latter observationsare not to be interpreted in any way as idenifying the character ofalloys in accordance with the invention, nor of course as anyexplanation of the improvement obtained.

Preferably the alloy in accordance with the invention comprisessignificant quantities of the additive elements but not more than about15 (weight) percent of each.

Where nickel and/or chromium are present the nickel content preferablylies between 3 and 12 (weight) percent and the chromium content between3 and 9 (weight) percent. A particularly suitable quinary alloy has thecomposition (weight)copper, 0.474; iron, 0.307; aluminium, 0.070;nickel, 0.074; chromium, 0.075. In this particular alloy it is foundthat the aluminium is distributed substantially equally between theiron-rich and copper-rich phases. Corrosion tests with this alloy haveshown that it possesses remarkable corrosion resistance, even whenexposed to marine conditions.

According to another aspect of the invention, an alloy which isbasically a matrix of a copper-rich solid solution phase containing 5 to10 (weight) percent of aluminium, the matrix containing an iron-richsolid solution phase which contains about 5 to 10 possibly up to 20(weight) percent of aluminium also includes both nickel and chromium.

Whereas in British Patent No. 1,137,123 referred to above, accent is onthe fibrous form of the iron-rich phase, it is not intended that thescope of the present invention should be limited to materials whereinthis phase has such a form. In the case of the quinary alloy mentionedabove, for example, it is found that, though the disperse iron-richphase is not of fibrous form the alloy possesses good mechanicalcharacteristics and at the same time is remarkably corrosion-resistantin both the worked state and as cast.

Inorder that the improvement obtained in a copper/ iron/aluminium alloyby exercise of the invention may be more clearly understood, referenceshould be made to Tables I and II below.

Table I shows the composition (weight percentage) of the basic alloytested-Alloy A and also those of a number of other similar alloys inwhich nickel and/ or chromium are includedAlloys B, F, G, H, I and K.These latter alloys are grouped together in that they represent a seriesof alloys in which the nickel content of the quinary is varied foraluminium and chromium contentsof substantially constant proportions.Table I also includes the compositions of other alloys Alloy D whichcontains nickel and chromium in substantially equal though comparativelylow proportions, Alloy M which is characterised by lower aluminiumcontent, Alloy L which contains carbon and Alloy C and Alloys E and Iwhich latter three alloys contain nickel and chromium respectively only.

The alloys of the invention range from being ferromagnetic tonon-magnetic and in colour from steel grey to champagne.

TABLE I Fe A1 C1. Ni O 4 proves roughly in .proportion to the amount ofnickel present. This may give some guide as to the choice of alloy for aparticular use. The tests for alloy M are continuing but this alloy isobviously particularly corrosion resistant. v

Alloyv D, possibly because the chromium and/0r nickel contents are low,shows up slightly less favourably than the others containing nickel andchromium.

Alloy L containing carbon is found to be heat-treatable after working sothat the hardness can be controlled; its corrosion resistance is good.Although Alloy C does not show up well in these very severe tests, it isfound to be reasonably tarnish resistant. Alloy I does not show upfavourably in comparison with Alloy A in the saline solution test, butit is nevertheless found to be very good from the point of being tarnishfree; it is highly suited to the production of household cutlery and, infact, appears to be a good substitute for stainless steel. For thisreason it and other alloys according to the invention may havearchitectural applications.

It appears that some of these alloys are readily hotrolled, some arereadily cold-rolled and some may be both hot-rolled and cold-rolled.

Specimens of Alloy B in the as-cast state have ultimate tensile strength(-U.T.S.) of about 53 tons per sq. in. with 0.1 percent proof stress{P.S.) of 28 tons per sq. in. and elongation of 17 percent. After coldIOllingto give a reduction in cross-sectional area of about 18 percent,with seven intermediate annealing heat treatments at 970 C., the U.T.S.was over 65 tons sq. in., the RS. 23.5 tons per sq. in. and theelongation about 7 percent.

In the worked state it is expected that the iron-rich phase of at leastsome of the alloys would take on a fibrous form and that the mechanicalproperties would be thereby enhanced as described in British patentspeci- Table II shows the results in terms of cumulative weight lossesin g./ sq. dm./year, after immersion of the particular alloys for agiven period of days in the as-east condition in stagnant 3% sodiumchloride solution.

It will be seen by comparison of the data for Alloys A and B that theefifect of the addition of nickel and chromium to the ternary alloy isremarkable.

In a hot-rolled state Alloy B showed only slight rust spots afterforty-two days in similar laboratory tests and it has been shown that,even after three months immersion, both in the as-cast and hot-rolledstates, Alloy B is still very much less rusted than Alloy A and, indeed,than any other ternary copper/iron/aluminium alloy of the basiccomposition which has been tested.

Both in the as-cast and hot-rolled states, Alloy B retains anuntarnished appearance on exposure to air indoors for six months atleast and this alloy would therefore be a useful decorative substitutefor brass which becomes quite dull under similar conditions within thistime.

Though the results shown in Table II for Alloys F, G, H, I and K are notentirely consistent, possibly because the compositions are not exactlycomparable, it is seen that the corrosion resistance of this group ofalloys imfication No. 1,137,123 referred to above. It is not essentialthat alloys in accordance with the invention should have that property.

We claim:

1. A copper/ iron/ aluminium alloy of the basic composition 35 to weightpercent copper, 20 to 50 weight percent iron and 5 to 15 weight percentaluminium and having a matrix of a copper-rich solid solution phasewhich contains a dispersed iron-rich solid solution phase, and in whichat least one alloying element selected from the group consisting ofnickel and chromium is additionally present to the extent of about 3 to15 percent by weight of the resultant alloy to ennoble the iron-richdispersed phase.

2. A copper/iron/aluminium alloy as claimed in claim 1, in which nickelis present as a said alloying element, the nickel content of theresultant alloy being in the range 3 to 12 percent.

3. A copper/iron/aluminium alloy as claimed in claim 1, in whichchromium is present as a said alloying element, the chromium content ofthe-resultant alloy being in the range 3 to 9 percent.

4. A copper/iron/aluminium alloy as claimed in claim 1, in which nickeland chromium are present as said alloying elements, the nickel contentof the resultant alloy being substantially in the range 3 to 12 percentand the chromium content being substantially in the range 3 to 5 9percent.

5. A copper/ iron/ aluminium alloy containing basically 35 to 75 weightpercent copper, 20 to 50 weight percent iron and 5 to 15 Weight percentaluminium and which is basically a matrix of a copper-rich solidsolution phase containing 5 to 10 Weight percent aluminium, the matrixcontaining an iron-rich solid solution phase which contains 5 to 20weight percent aluminium, the alloy also including nickel and chromiumeach to the extent of from about 3 to 15 percent by weight of theresultant alloy. 15

References Cited UNITED STATES PATENTS 1,369,818 3/1921 Kosugi 75-162 X2,027,997 1/1936 Mishima 75-122 3,384,517 5/1968 Harper et a1. 14831 XOTHER REFERENCES Transactions of AIME, vol. 180, 1949, pp. 32-37.

CHARLES N. LOVELL. Primary Examiner US. Cl. X.R.

